Tear secretion by the eye protects and maintains the integrity of ocular surface tissues including the cornea, corneal limbus, conjunctiva, blood vessels, and eyelids. Tear secretion is crucial to protecting the eye from infectious agents and environmental damage. The liquid film formed by tears is also essential to providing a smooth optical surface and to maintaining cellular health.
One of the most common ophthalmic conditions is dry eye syndrome (also known as keratoconjunctivitis sicca and “dry eye”). Dry eye is defined by a deficiency or lack of tears which can lead to inflammation and damage to the eye.
Dry eye can have numerous causes. For example, a temporary form of dry eye can be triggered by an inflammatory reaction to eye trauma or infection. In some, temporary dry eye can become chronic, for example, when a local ocular autoimmune condition develops.
Dry eye can also be caused by systemic conditions. For example, Sjogren's syndrome is an autoimmune disorder identified by its two most common symptoms, dry eyes and a dry mouth. Sjogren's syndrome results in immune system damage to the mucous membranes and moisture-secreting glands of the eyes and mouth. The cell and tissue damage results in decreased production of tears and saliva. Sjogren's syndrome often accompanies other immune system disorders, such as rheumatoid arthritis and lupus erythematosus.
Current treatments for dry eye caused by Sjogren's syndrome include pharmaceuticals such as Pilocarpine, cyclosporine or Cevimeline, both of which primarily increase saliva production when used orally. Pilocarpine can be administered as eye drops, but constriction of the pupil and the risk of epileptic-type effects have to be considered.
Sjogren's syndrome is just one example of a condition that leads to dry eye that lacks an effective treatment without unacceptable side effects. As another example, uveitis, inflammation of the uvea, is responsible for about 10% of visual impairment in the United States. The uveal tract includes the iris, ciliary body, and choroid. Uveitis is most commonly classified anatomically as anterior, intermediate, posterior, or diffuse. Anterior uveitis is localized primarily to the anterior segment of the eye and includes iritis and iridocyclitis. Intermediate uveitis, also called peripheral uveitis, is centered in the area immediately behind the iris and lens in the region of the ciliary body and pars plana, hence the alternate terms “cyclitis” and “pars planitis” are also used. Posterior uveitis signifies a number of forms of uveitis including retinitis, choroiditis, and optic neuritis. Diffuse uveitis implies inflammation involving all parts of the eye, including anterior, intermediate, and posterior structures. Current treatments for uveitis include principally locally applied and/or systemic steroid therapy.
Approximately 6% of uveitis cases in the United States occur in children, while 2.2-33.1% of uveitis cases in international populations occur in children and adolescents. One of the major causes of pediatric uveitis is associated with autoimmune disorders including: juvenile idiopathic arthritis, reactive arthritis, ankylosing spondylitis, ulcerative colitis, Crohns disease, childhood sarcoidosis, and Kawasaki disease. Pediatric uveitis is a major health concern in children, as complications include band keratopathy, glaucoma, phthisis, cataract formation, macular edema, and optic nerve degeneration. Chronic uveitis can result in morbidity and vision loss.